Messenger once covered by other messengers (6)
I believe the answer is:
hermes
'messenger' is the definition.
(Greek messenger god)
'covered by other messengers' is the wordplay.
'covered by' indicates a hidden word.
'HERMES' can be found hidden inside 'other messengers'.
'once' is the link.
(Other definitions for hermes that I've seen before include "Greek messenger god" , "Winged messenger" , "Greek god of commerce and theft" , "Messenger and herald of the gods" , "Greek messenger of the gods, like Roman Mercury" .)